pool

Load Distribution Facility

pool can be used to run a set of Erlang nodes as a pool
of computational processors. It is organized as a master and a
set of slave nodes and includes the following features:

The slave nodes send regular reports to the master about
their current load.Queries can be sent to the master to determine which node
will have the least load.

The BIF statistics(run_queue) is used for estimating
future loads. It returns the length of the queue of ready to run
processes in the Erlang runtime system.

The slave nodes are started with the slave module. This
effects, tty IO, file IO, and code loading.

If the master node fails, the entire pool will exit.

Functions

start(Name) ->

start(Name, Args) -> Nodes

Name = atom()

Args = string()

Nodes = [node()]

Starts a new pool. The file .hosts.erlang is read to
find host names where the pool nodes can be started. See
section Files below. The
start-up procedure fails if the file is not found.

The slave nodes are started with slave:start/2,3,
passing along Name and, if provided, Args.
Name is used as the first part of the node names,
Args is used to specify command line arguments. See
slave(3).

Access rights must be set so that all nodes in the pool have
the authority to access each other.

The function is synchronous and all the nodes, as well as
all the system servers, are running when it returns a value.

attach(Node) -> already_attached | attached

Node = node()

This function ensures that a pool master is running and
includes Node in the pool master's pool of nodes.

stop() -> stopped

Stops the pool and kills all the slave nodes.

get_nodes() -> Nodes

Nodes = [node()]

Returns a list of the current member nodes of the pool.

pspawn(Mod, Fun, Args) -> pid()

Mod = Fun = atom()

Args = [term()]

Spawns a process on the pool node which is expected to have
the lowest future load.

pspawn_link(Mod, Fun, Args) -> pid()

Mod = Fun = atom()

Args = [term()]

Spawn links a process on the pool node which is expected to
have the lowest future load.

get_node() -> node()

Returns the node with the expected lowest future load.

Files

.hosts.erlang is used to pick hosts where nodes can
be started. See
net_adm(3)
for information about format and location of this file.

$HOME/.erlang.slave.out.HOST is used for all additional IO
that may come from the slave nodes on standard IO. If the start-up
procedure does not work, this file may indicate the reason.